Research has shown that some patients who suffer from anxiety attacks and/or panic disorders are extremely sensitive to small variations in carbon dioxide (CO2) levels. The known elevation of CO2 in closed-in, agoraphobic or claustrophobic environments is one causative factor of panic attacks in patients diagnosed with panic disorder. Panic attacks resemble suffocation. Panic attack patients have lower blood CO2 and are more sensitive to increases of CO2.
Anxiety has been defined as a feeling of fear, dread or apprehension that arises without clear or appropriate justification. Anxiety includes a number of symptoms that are physical, psychological and behavioral in nature. Anxiety during a panic attack may manifest itself in a number of physical signs that are typically produced from over-activity of the sympathetic nervous system or even from tension in the skeletal muscles. These physical manifestations include palpitations, dry mouth, and dilation of the pupils, sweating, throat tightening, trembling, dizziness and even nausea. Psychological manifestations include irritability, restlessness and loss of concentration. Behavioral manifestations primarily include avoidance behavior, such as running away from a feared object or situation.
The effects of elevated levels of inspired carbon dioxide on the human brain have been studied. Specifically, carbon dioxide's local tissue vasodilatation effect is the major factor affecting cerebral blood flow. In healthy people, low concentrations of inspired CO2 have been found to produce central nervous system stimulation. For example, the administration of 5% CO2 has been shown to produce mental confusion, brain vasodilatation, elevated blood pressure and pulse, increased myocardial contractility and constriction of skeletal muscles. Concentrations of 10% or higher have a central nervous system depressant effect in healthy people and may lead to loss of consciousness within as little as 10 minutes. At concentrations of 30%, carbon dioxide becomes an anesthetic.
As shown in FIG. 1, analysis of air samples taken from environments commonly avoided by individuals with a panic disorder have shown increased levels of CO2 up to 315% higher than normal outside air. The level of CO2 in outside air is typically 0.03% or 300 ppm (parts per million). As shown in FIG. 1, the highest levels of CO2 recorded, i.e., just below 0.1% or 1,000 ppm, were collected in a medical center elevator with 10 passengers, an automobile with 3 persons inside and no open windows, and a small jet aircraft fully loaded with passengers and the exit door closed. Typical elevated CO2 levels of 0.06% or 600 ppm to 0.075% or 750 ppm, twice that of outside air, were collected in a range of environments such as restaurants, conference rooms, church services and classrooms.
At the onset of an anxiety attack a patient may use an inhalation device to lower the amount of CO2 sensed by the individual. Patients may use a portable device containing CO2 adsorbent through which to inhale at the onset of experiencing symptoms of their disorder. The adsorbent may reduce inspired CO2 levels from the elevated level experienced in the current environment. Reducing inspired CO2 levels may, in whole or in part, alleviate a panic attack and, thereby, accommodate the patients' disability. Of paramount importance is that the device offers the lowest possible breathing resistance and minimizes the risk of inhaling adsorbent particulates, while offering excellent CO2 adsorption.
Traditional CO2 adsorbents are typically manufactured by mixing hydrated lime with water and optionally a small amount of sodium or potassium hydroxide to form a paste, which is then extruded or molded in particles in granular or pellet form. These soda lime adsorbents are typically used in rebreather devices such as anesthesia machines and underwater breathing systems, where expired breath passes through a canister filled with adsorbent material where it is cleansed of CO2, before being inhaled by a user. Soda lime adsorbents have limited value for individual inhalation devices because they have a limited ability to adsorb CO2 when the devices for adsorption are small in size.
Adsorbent granules or pellets are loaded into a rebreather device in loose particulate form by pouring into an adsorber or supplied in pre-packed disposable containers for insertion into the adsorber. Adsorbent granules or pellets are generally sized between about 0.04 to 0.25 inches (1.0 to 6.5 mm) in diameter.
To achieve minimal breathing resistance, larger adsorbent particles are employed to allow gas flow around the granules, which offers a relatively low-pressure drop. Smaller granules allow more surface area per unit weight for greater CO2 adsorption, however, an increase in breathing resistance in experienced.
Granules by their very nature are different shapes and sizes leading to variable performance, non-uniform depletion, channeling, strike through and wastage of un-exhausted granules. Additionally, granules have a tendency to grind together when packed and when being transported, which produces particulates or dust. Space consuming filters can be introduced to minimize inhalation of particulates; however, this introduces an unwanted resistance to breathing.
The ongoing trade-off between CO2 removal rate, low-pressure drop, high CO2 absorption capacity and size of adsorbent bed is a major limitation of granules. Granule manufacturers have tried to address these limitations by introducing alternative shapes and different formulations; however, the inherent flaws still exists.
Needs exist for improved adsorbents and inhalation devices that use improved adsorbents.